The São João stream is the strategic source for supplying the municipal headquarters of Porto Nacional. This dissertation aimed to identify the main risks and vulnerabilities to the public supply of Porto Nacional / TO, associated to the quantity and quality of raw water of the Córrego São João basin, and to analyze the level of current and future water security of the municipality. We adopted the model developed by members of the Research Group "Water, Water Management and Safety in times of Global Environmental Change".Thus, it was possible to develop a methodology of analysis of water security of urban supplies, specific to the São João Stream basin in Porto Nacional / TO, considering four stress factors considered as the most determinant for current vulnerability: i) pressure On environmental conditions; Ii) demand for water; (Iii) pollutant load and (iv) extreme hydrological events. The results showed that the greatest stressor to the water security of the supply of Porto Nacional, related to the problems of quantity and quality of raw water, is the demand for water. On the other hand, the pressure on the environmental conditions of the Basin was evidenced by the preparation and analysis of maps of land use and occupation in 2006, 2011 and 2016; The evolution (in time and space) of the anthropic occupation with implantation of temporary crops and of pastures, besides the notorious urban expansion, was verified. We did not identify any records of total paralysis of ETA 02. The main result shows that, currently, there is still compatibility between the quali-quantitative availability of the raw water of the São João Stream and the subsystems of capture and treatment of ETA 02.
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